JP5642737B2 - Insulation diagnostic device, insulation diagnostic system, program - Google Patents

Description

  The present invention relates to an insulation diagnosis apparatus, an insulation diagnosis system, and a program.

  In an AC circuit on the secondary side of the transformer, in order to prevent the ground voltage on the secondary side of the transformer from becoming high, generally, a predetermined bus of the AC circuit is grounded (see, for example, Patent Document 1).

JP 2007-28813 A

  By the way, of the AC circuit bus, if a ground fault occurs on the ungrounded bus, and the resistance value between the ungrounded bus is reduced, the ground fault (insulation resistance) Can be detected. However, since the resistance between the grounded bus and the ground is small, the ground voltage is low, and it is difficult to detect a ground fault of the ground-side bus with an earth leakage breaker or the like. Therefore, conventionally, insufficiency of the bus on the ground side of the AC circuit has been inspected in a state where a part of the system is blacked out and the operation of the AC circuit is stopped.

  The present invention has been made in view of the above problems, and provides an insulation diagnostic apparatus capable of diagnosing the insulation state of the ground-side busbar while the AC circuit is operating.

In order to achieve the above object, an insulation diagnostic apparatus according to one aspect of the present invention includes a power source side first bus connected to a secondary side of a first transformer, and a secondary side of the first transformer. A control device to which a measurement result of a zero-phase current transformer that measures a zero-phase current of the first bus and the second bus of an AC circuit including a second bus on the ground side to be connected is input, and a primary side One end of the second side and one end of the secondary side are connected to the second busbar, the other end of the secondary side is grounded, the other end of the primary side in the second transformer and the second A first switch provided between one bus and a second switch provided between one end of the secondary side and the other end of the secondary side of the second transformer , control device includes a control unit for controlling the state of said first and second switches, wherein provided on the secondary side of the first transformer In a state where the wiring is removed to ground 2 bus, the first switch is turned off, the first current value and the first voltage value of the first generatrix of said zero-phase current of the second switch is turned on and An acquisition unit that acquires a second current value of the zero-phase current and a second voltage value of the first bus when the first switch is on and the second switch is off; and A calculation unit that calculates a current flowing through the resistance between the grounds when a predetermined voltage is applied to the resistance between the grounds of the second bus based on the acquired results.

  Provided is an insulation diagnostic device capable of diagnosing an insulation state of a ground-side busbar while an AC circuit is operating.

It is a figure which shows the outline | summary of the alternating current circuit 10 provided with the insulation diagnostic system 30 which is one Embodiment of this invention. It is a figure which shows an example of the functional block implement | achieved by the microcomputer 72. FIG. It is a figure for demonstrating the state of switch S1, S2 of the transformer 50 at the time of an insulation diagnostic process being performed. It is a figure for demonstrating the state of switch S1, S2 of the transformer 50 at the time of an insulation diagnostic process being performed. It is a figure which shows an example in case the ground fault has generate | occur | produced in the neutral pole of AC circuit. It is a flowchart which shows an example of an insulation diagnostic process.

  At least the following matters will become apparent from the description of this specification and the accompanying drawings.

FIG. 1 is a diagram showing an outline of an AC circuit 10 provided with an insulation diagnosis system 30 according to an embodiment of the present invention.
The AC circuit 10 is a single-phase three-wire circuit that steps down a voltage from a high voltage (distribution line), and includes a transformer 20, circuit breakers 21 to 23, buses 25 to 27, and wiring 28.

  The transformer 20 is a transformer that steps down the voltage from the high voltage applied to the primary side and outputs it to the secondary side. For example, 110V (effective value) AC voltage having opposite phases is output between the terminals A1 and A2 on the secondary side of the transformer 20 and between the terminals A2 and A3.

  The buses 25 and 26 are power source side buses connected to the terminals A1 and A3 via the circuit breakers 21 and 23, respectively. The bus 27 is a ground-side bus connected to the terminal A2 (neutral point) via the circuit breaker 22. Here, the terminal A2 is grounded via the wiring 28 so that the ground voltage of the AC circuit 10 does not become too high. Although details will be described later, when the insulation diagnostic device 41 is provided in the AC circuit 10 and the insulation diagnostic device 41 is connected to each bus, the wiring 28 is removed. Various devices such as a relay (not shown) are connected as loads between the buses 25 and 26 and between the buses 25 and 27. The AC circuit 10 includes a circuit constituted by the bus 25 and the bus 27 and a circuit constituted by the bus 26 and the bus 27. In the present embodiment, for the sake of convenience, the AC circuit 10 is constituted by the bus 25 and the bus 27 hereinafter. The explanation will be focused on the AC circuit.

  The insulation diagnosis system 30 is a device that diagnoses the insulation state of the ground-side bus bar 27 of the AC circuit 10, and includes a zero-phase current transformer 40 and an insulation diagnosis device 41.

  The zero-phase current transformer 40 is a current transformer that measures a current Ix (leakage current) flowing from the buses 25 and 27 to the ground by clamping the two buses of the buses 25 and 27.

  The insulation diagnostic device 41 is a device for diagnosing the insulation state of the ground-side bus 27 based on the measurement result of the zero-phase current transformer 40, and includes a transformer 50, a control device 51, and switches S1 and S2. Composed.

The transformer 50 is a transformer for applying a predetermined voltage to the bus 27 on the ground side, and terminals N1 and N2 are provided on the primary side, and terminals N3 and N4 are provided on the secondary side. Yes.
In the transformer 50, the primary-side terminal N1 (one end) and the secondary-side terminal N3 (one end) are both connected to the ground-side bus 27. Further, the transformer 50 is configured such that when 110V AC voltage is generated between the primary side terminals, the number of turns on the primary side and the secondary side so that 40V AC voltage is generated between the secondary side terminals. Is stipulated. 110V and 40V are both effective values.

The switch S1 (first switch) is a switch for connecting the primary terminal N2 (the other end) of the transformer 50 to any one of the buses 25 to 27 or setting the open state.
The switch S2 (second switch) is a switch for setting a short circuit state or an open state between the terminals N3 and N4 on the secondary side of the transformer 50.

  The control device 51 controls the states of the switches S1 and S2 and calculates a current I1 flowing from the ground-side bus 27 to the ground. The control device 51 includes an AD converter 70, a storage device 71, a microcomputer 72, a display device 73, and an alarm device 74.

The AD converter 70 digitizes the measurement results of the zero-phase current transformer 40 and the voltages of the buses 25 and 26 and outputs them to the microcomputer 72.
The storage device 71 stores a program executed by the microcomputer 72, measurement data, and the like.
The microcomputer 72 implements various functions by executing a program stored in the storage device 71, and performs overall control of the control device 51.
The display device 73 displays the result of processing executed by the microcomputer 72 and various information, and the alarm device 74 sounds an alarm (for example, an alarm) when the leakage current from the ground bus 27 is larger than a predetermined value.

<< Function Blocks of Microcomputer 72 >>
FIG. 2 is a diagram illustrating an example of functional blocks executed by the microcomputer 72. In the microcomputer 72, a control unit 80, an acquisition unit 81, a calculation unit 82, a determination unit 83, an alarm output unit 84, and a display unit 85 are realized.

  The control unit 80 controls the states of the switches S1 and S2. Specifically, as shown in FIG. 3, the control unit 80 switches the switch S1 so that the primary terminal N2 of the transformer 50 is short-circuited with the terminal N1, and the secondary terminal N3 of the transformer 50 is The switch S2 is turned on so as to short-circuit the terminal N4. Further, as shown in FIG. 4, the control unit 80 switches the switch S <b> 1 so that the primary side terminal N <b> 2 of the transformer 50 is connected to the power source side bus 25, and the secondary side terminal N <b> 3 of the transformer 50. , N4, the switch S2 is turned off. Hereinafter, the state of the switches S1 and S2 illustrated in FIG. 3 is referred to as state 1, and the state of the switches S1 and S2 illustrated in FIG.

  The acquisition unit 81 acquires the current Ix1 measured by the zero-phase current transformer 40 when the switches S1 and S2 are in the state 1, and the voltage Vx1 of the bus 25. Furthermore, the acquisition unit 81 acquires the current Ix2 measured by the zero-phase current transformer 40 and the voltage Vx2 of the bus 25 when the switches S1 and S2 are in the state 2.

  The calculation unit 82 uses the currents Ix1 and Ix2 and the voltages Vx1 and Vx2 to calculate a current I1 that flows from the bus 27 to the ground when a predetermined voltage (for example, 110 V) is applied to the ground-side bus 27. . Each time the calculation unit 82 calculates the current I1, the calculation unit 82 stores the calculated current I1 and information indicating the calculated time in the storage device 71.

  In the following description, it is assumed that the insulation resistance R1 connected to the bus 25 is 1.1 MΩ, the insulation resistance R2 connected to the bus 27 and the ground fault resistance Rg are 1.1 MΩ and 0.1 MΩ, respectively. Here, the wiring 28 previously connected to the terminal A2 of the transformer 20 has been removed by an operator or the like. Even in such a case, since the AC circuit 10 is grounded via the secondary terminal N4 of the transformer 50, a high ground voltage is not generated in the AC circuit 10.

First, when the switches S1 and S2 shown in FIG. 3 are in the state 1, since the primary side and the secondary side of the transformer 50 are short-circuited, the transformer 50 does not transform the input voltage. Since the bus 27 is grounded via the turned-on switch S2, the voltage of the bus 27 is 0V. On the other hand, since the AC voltage generated between the buses 25 and 27 is 110 V (effective value), the voltage of the bus 25 is also 110 V (effective value). Therefore, in this case, the current Ix1 measured by the zero-phase current transformer 40 is only the current that flows from the insulation resistance R1 of the bus 25 to the ground. That is, the current Ix1 is
Ix1 = 110V / (1.1MΩ) = 0.1 mA (1)
It becomes. At this time, the voltage Vx1 of the bus 25 is 110V.

  Next, when the switches S1 and S2 shown in FIG. 4 are in the state 2, the primary-side terminal N2 of the transformer 50 is connected to the bus 25, and the secondary-side terminals N3 and N4 are opened. In this case, since the voltage generated on the primary side of the transformer 50 is equal to 110V generated between the buses 25 and 27, the voltage generated on the secondary side of the transformer 50 is 40V as described above. . Further, since the terminal N4 of the transformer 50 is grounded, the voltage of the ground side bus 27 is 40V, and the voltage of the power source side bus 25 is 150V (= 40V + 110V).

Therefore, the current Ix2 is the sum of the current flowing from the insulation resistance R1 of the bus 25 to the ground and the current flowing from the insulation resistance R2 of the bus 27 and the ground fault resistance Rg to the ground. That is, the current Ix2 is
Ix2 = 150V / (1.1MΩ) + 40V / (1.1MΩ // 0.1MΩ)
= 0.5728 mA (2)
It becomes. In addition, 1.1 MΩ // 0.1 MΩ is the value of the parallel resistance (resistance between the ground) of the resistors R2 and Rg. Further, the voltage Vx2 is 150V.

  Thus, the calculation unit 82 acquires the currents Ix1 and Ix2 in FIGS. Then, the calculation unit 82 determines a predetermined value for the bus 27 based on the currents Ix1 (first current value) and Ix2 (second current value) and the voltages Vx1 (first voltage value) and Vx2 (second voltage value). A current I1 flowing from the bus 27 to the ground when the voltage (110 V) is applied is calculated.

First, the calculation unit 82 calculates a current IA flowing from the bus 27 to the ground in the state of FIG. Specifically, as shown in Expression (3), the current flowing through the insulation resistance R1 in the state of FIG. 4 is calculated from the current Ix1, and subtracted from the current Ix2.
IA = Ix2-Ix1 × (Vx2 / Vx1) (3)
= 0.5728−0.1 × (150/110) ≈0.4364 mA

The current IA is a current IA that flows from the bus 27 to the ground in the state of FIG. Then, calculation unit 82 calculates current I1 when voltage 110V is applied to bus 27 based on current IA.
I1 = IA × (Vx1 / (Vx2−Vx1)) (4)
= 0.4364 × (110/40) ≈1.2 mA

  That is, if a ground fault occurs on the bus 27 and the ground fault resistance Rg is connected, if a high voltage (110 V) is applied to the bus 27, a large current I1 is generated as shown in equation (4). It will flow. Such a current I1 may flow, for example, when a ground fault occurs at a location (neutral pole) as shown in FIG.

  FIG. 5 is a diagram illustrating a state in which a ground fault has occurred in the nodes P1 and P2. Here, since the insulation diagnostic device 41 and the like are removed, the bus bar 27 is grounded via the wiring 28. Note that ground fault resistors Rga and Rgb having a resistance value of 0.1 MΩ are equivalently connected to the nodes P1 and P2, respectively. A relay 100 and a switch 110 connected in series are connected between the buses 25 and 27. For this reason, for example, a ground fault occurs in the ground bus 27. When the switch 110 is turned on (turned on), 110 V is applied to the node P1, and therefore, a leakage current (zero phase current) of about 1.0 mA flows through the AC circuit 10.

  In addition, a relay 101 and switches 111 and 112 connected in series are connected between the buses 25 and 27. For this reason, for example, when the switch 111 is turned on, a ground fault has occurred in the bus 27 on the ground side. When the switch 112 is turned on, 110 V is applied to the node P2, so that a leakage current of about 1.0 mA flows through the AC circuit 10. The insulation diagnostic system 30 is connected to the AC circuit 10 in which a ground fault has occurred at the nodes P1 and P2 (in the case of the node P2, the switch 111 or the switch 112 is operating), and the current I1 is calculated. Then, the current I1 shown in Expression (4) is obtained.

  The determination unit 83 in FIG. 2 determines whether or not the current value of the current I1 calculated by the calculation unit 82 is greater than a predetermined value IAL (for example, 0.5 mA).

  The alarm output unit 84 causes the alarm device 74 to output an alarm (for example, an alarm) when the value of the current I1 is larger than the predetermined value IAL.

  The display unit 85 causes the display device 73 to display an alarm display when the value of the current I1 is larger than the predetermined value IAL. Further, the display unit 85 causes the display device 73 to display a caution display indicating that there is a sign that the insulation resistance of the bus bar 27 is decreasing, even if the alarm display is not displayed on the display device 73. Specifically, the display unit 85 calculates the current value of the calculated current I1 continuously increased n times (for example, 10 times) or more, that is, the current I1 calculated last time and the current value calculated this time. The current I1 is compared, and if the current I1 calculated this time is greater than n times, a caution display is displayed.

== Example of insulation diagnosis processing ==
FIG. 6 is a flowchart showing an example of processing executed by the microcomputer 72 when performing insulation diagnosis of the bus 27. Here, in the AC circuit 10 shown in FIG. 1, the wiring 28 is removed, and the zero-phase current transformer 40 and the insulation diagnostic device 41 are attached to the AC circuit 10. Moreover, the insulation diagnostic apparatus 41 installed in the AC circuit 10 executes an insulation diagnosis process, for example, periodically (for example, every predetermined number of days).

  First, when the insulation diagnostic apparatus 41 starts diagnosis processing according to an instruction from an operator or the like, the control unit 80 sets the switches S1 and S2 to the first state (the state shown in FIG. 3) (S100). Then, the acquisition unit 81 acquires the current Ix1 and the voltage Vx1 when the switches S1 and S2 are in the state 1 (S101). When the current Ix1 or the like is acquired, the control unit 80 changes the state of the switches S1 and S2 to the second state (the state of FIG. 4) (S102). When the states of the switches S1 and S2 change, the acquisition unit 81 acquires the current Ix2 and the voltage Vx2 (S103). Further, the calculation unit 82 calculates the leakage current when the voltage 110V is applied to the bus 27, that is, the current I1 flowing from the bus 27 to the ground by calculating the equations (3) and (4). (S104).

  The determination unit 83 determines whether or not the calculated current value of the current I1 is greater than a predetermined value IAL (S105). When the current value of the current I1 is larger than the predetermined value IAL (S105: YES), the alarm output unit 84 causes the alarm device 74 to output an alarm (S106). On the other hand, when the current value of the current I1 is smaller than the predetermined value IAL (S105: NO), the calculation unit 82 stores the calculated current I1 and information indicating the calculated time in the storage device 71 (S107). . Further, the display unit 85 determines whether or not the calculated current value of the current I1 has increased continuously n times (for example, 10 times) or more (S108). When the current I1 continuously increases n times or more (S108: YES), the display unit 85 displays a caution display on the display device 73 (for example, a panel) (S109). On the other hand, if the current I1 has not increased continuously n times or more (S108: NO), the insulation diagnosis process is terminated.

  In the above, the insulation diagnostic system 30 which is one Embodiment of this invention was demonstrated. The insulation diagnostic device 41 can calculate a current I1 (leakage current) that flows from the bus 27 to the ground when a predetermined voltage is applied to the ground-side bus 27 while the AC circuit 10 is operating. That is, the insulation diagnostic device 41 can diagnose the insulation state of the bus 27 on the ground side even when the AC circuit 10 is in operation. For this reason, it is possible to prevent an unnecessary power failure from occurring in the system in which the AC circuit 10 is provided. Therefore, it is possible to detect the presence or absence of a ground fault occurring at the neutral pole (nodes P1 and P2 shown in FIG. 5), which is conventionally difficult to diagnose the insulation state.

  The alarm device 74 outputs an alarm when the current value of the current I1 is larger than the predetermined value IAL, that is, when the insulation of the bus 27 on the ground side is deteriorated. For this reason, the user can immediately grasp that a ground fault or the like has occurred in the AC circuit 10.

  Further, the storage device 71 sequentially stores information on the current I1 and time. For this reason, the user can grasp | ascertain the correlation with the time change (trend) and the weather conditions of the insulation state of the bus-line 27 on the ground side based on such information.

  Further, when the calculated value of the current I1 continuously increases n times or more, that is, when the value of the current I1 gradually increases, a caution display is displayed on the display device 73. For this reason, the user can grasp that the insulation state has deteriorated.

  In the present embodiment, the zero-phase current transformer 40 is provided so as to clamp the buses 25 and 27. However, for example, a similar zero-phase current transformer may be provided on the buses 26 and 27 as well. In this case, the insulation diagnosis device 40 can obtain the voltage of the bus 26 to perform insulation diagnosis of the AC circuit formed by the buses 26 and 27. Moreover, although AC circuit 10 of the present embodiment is a single-phase three-wire circuit, it is not limited thereto. For example, a single-phase two-wire circuit or a three-phase three-wire circuit may be used.

  Further, in order to use the insulation diagnosis system 30 for the AC circuit 10, it is only necessary to remove only the grounding wire on the secondary side of the transformer 20 in the AC circuit 10, that is, the wiring 28 for grounding the terminal A2. Therefore, the insulation diagnostic system 30 can be used for an existing general AC circuit.

  In the present embodiment, the secondary terminal N4 of the transformer 50 is always grounded. For this reason, a high ground voltage is not generated in the AC circuit 10. Furthermore, the turn ratio of the transformer 50 is adjusted so that the voltage on the secondary side of the transformer 50 is 40V. For this reason, the AC circuit 10 can be diagnosed at 150 V or less determined by a predetermined electrotechnical standard.

  In addition, the said Example is for making an understanding of this invention easy, and is not for limiting and interpreting this invention. The present invention can be changed and improved without departing from the gist thereof, and the present invention includes equivalents thereof.

  In the present embodiment, the voltages Vx1 and Vx2 are measured and acquired, but the present invention is not limited to this. The voltage Vx1 is a voltage generated at the terminals A1 and A2 on the secondary side of the transformer 20, and the voltage Vx2 is determined by the turn ratio of the transformer 50. Therefore, the voltage of the bus 25 in each of the states 1 and 2 may be stored in the storage device 71 in advance and acquired by the acquisition unit 81. However, the current I1 can be calculated with higher accuracy when the acquisition unit 81 measures the result of actually measuring the voltage of the bus 25.

  In the process of FIG. 6, the insulation diagnosis system 30 is permanently installed in the AC circuit 10 and the insulation diagnosis is periodically performed. However, the present invention is not limited to this. For example, the insulation diagnosis may be executed only when the insulation diagnosis system 30 is installed.

  In addition, as the transformer 50, a single-phase compound winding transformer in which the primary side terminal N1 and the secondary side terminal N3 are short-circuited is used. Also good.

DESCRIPTION OF SYMBOLS 10 AC circuit 20,50 Transformer 21-23 Circuit breaker 25-27 Bus line 28 Wiring 30 Insulation diagnostic system 40 Zero phase current transformer 41 Insulation diagnostic apparatus 51 Control apparatus 70 AD converter (ADC)
71 Storage Device 72 Microcomputer 73 Display Device 74 Alarm Device 80 Control Unit 81 Acquisition Unit 82 Calculation Unit 83 Determination Unit 84 Alarm Output Unit 85 Display Unit S1, S2 Switch

Claims (7)

The first bus of the AC circuit including a first bus on the power supply side connected to the secondary side of the first transformer and a second bus on the ground side connected to the secondary side of the first transformer; A control device to which a measurement result of a zero-phase current transformer for measuring a zero-phase current of the second bus is input;
A second transformer in which one end on the primary side and one end on the secondary side are connected to the second bus, and the other end on the secondary side is grounded;
A first switch provided between the other end of the primary side of the second transformer and the first bus;
A second switch provided between one end on the secondary side and the other end on the secondary side of the second transformer ;
With
The controller is
A control unit for controlling states of the first and second switches;
The zero-phase current in a state in which the first switch is turned off and the second switch is turned on in a state where the wiring for grounding the second bus provided on the secondary side of the first transformer is removed. And the first voltage value of the first bus, the second current value of the zero-phase current and the first bus value of the first bus when the first switch is on and the second switch is off. An acquisition unit for acquiring two voltage values;
Based on the acquisition result acquired by the acquisition unit, a calculation unit that calculates a current flowing through the resistance between the ground when the predetermined voltage is applied to the resistance between the ground of the second bus,
An insulation diagnostic apparatus comprising: The insulation diagnostic device according to claim 1,
The controller is
A determination unit that determines whether or not the current ground of the current flowing through the resistance between the ground is larger than a predetermined value;
When it is determined that the current value of the current flowing through the resistance between the ground is larger than the predetermined value, an alarm output unit that outputs an alarm to the alarm device;
An insulation diagnostic apparatus further comprising: The insulation diagnostic device according to claim 1 or 2,
Each time the calculation unit calculates the current flowing through the resistance between the ground, information indicating the time when the current flowing through the resistance between the ground is calculated, and the current value of the current flowing through the calculated resistance between the ground And further comprising a storage unit for storing
Insulation diagnostic device characterized by. The insulation diagnostic device according to claim 3,
The controller is
A display unit that displays a predetermined display on a display device when the current value of the current flowing through the resistance between the ground sequentially stored in the storage unit continuously increases a predetermined number of times or more;
Insulation diagnostic device characterized by. The insulation diagnostic apparatus according to any one of claims 1 to 4,
The second bus is a neutral wire of single-phase three-wire electric wires,
The first bus bar is any one of electric wires different from the neutral wire of the single-phase three-wire electric wire;
Insulation diagnostic device characterized by. The first and second AC circuits including a power source side first bus connected to the secondary side of the first transformer and a ground side second bus connected to the secondary side of the first transformer . A zero-phase current transformer for measuring the zero-phase current of the two busbars;
A control device to which the measurement result of the zero-phase current transformer is input;
A second transformer in which one end on the primary side and one end on the secondary side are connected to the second bus, and the other end on the secondary side is grounded;
A first switch provided between the other end of the primary side of the second transformer and the first bus;
A second switch provided between one end on the secondary side and the other end on the secondary side of the second transformer ;
With
The controller is
A control unit for controlling states of the first and second switches;
The zero-phase current in a state in which the first switch is turned off and the second switch is turned on in a state where the wiring for grounding the second bus provided on the secondary side of the first transformer is removed. And the first voltage value of the first bus, the second current value of the zero-phase current and the first bus value of the first bus when the first switch is on and the second switch is off. An acquisition unit for acquiring two voltage values;
Based on the acquisition result acquired by the acquisition unit, a calculation unit that calculates a current flowing through the resistance between the ground when the predetermined voltage is applied to the resistance between the ground of the second bus,
Insulation diagnostic system comprising: The first and second AC circuits including a power source side first bus connected to the secondary side of the first transformer and a ground side second bus connected to the secondary side of the first transformer . A computer to which the measurement result of the zero-phase current transformer for measuring the zero-phase current of the two buses is input;
A second transformer in which one end on the primary side and one end on the secondary side are connected to the second bus, and the other end on the secondary side is grounded;
A first switch provided between the other end of the primary side of the second transformer and the first bus;
A second switch provided between one end on the secondary side and the other end on the secondary side of the second transformer ;
In the computer of the insulation diagnostic apparatus comprising:
A function of controlling the states of the first and second switches;
The zero-phase current in a state in which the first switch is turned off and the second switch is turned on in a state where the wiring for grounding the second bus provided on the secondary side of the first transformer is removed. And the first voltage value of the first bus, the second current value of the zero-phase current and the first bus value of the first bus when the first switch is on and the second switch is off. A function of acquiring two voltage values;
Based on the first and second current values and the first and second voltage values, a current that flows through the ground resistance when a predetermined voltage is applied to the ground resistance of the second bus A function for calculating
A program that realizes

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